Applied Vegetation Science 17 (2014) 591–603 SPECIAL FEATURE: VEGETATION SURVEY Grassland vegetation of the Molinio-Arrhenatheretea class in the NW Balkan Peninsula Urban Silc, Svetlana Acic, Zeljko Skvorc, Daniel Krstonosic, Jozo Franjic & Zora Dajic Stevanovic Keywords Balkan region; Classification; Europe; Grassland; Mesic meadows; Pastures; Phytosociology; Vegetation survey Nomenclature Vascular plants Tutin et al. (1964–1993) except for Scirpus georgianus Harper; Higher syntaxa Mucina et al. (2014) Received 10 July 2013 Accepted 7 December 2013 Co-ordinating Editor: Milan Chytry Silc, U. (corresponding author, urban@zrc-sazu.si): ZRC SAZU, Institute of Biology, Novi trg 2, 1000, Ljubljana, Slovenia; Biotechnical Centre Naklo, Strahinj 99, 4202, Naklo, Slovenia Acic, S. (acic@agrif.bg.ac.rs) & Dajic Stevanovic, Z. (dajic@agrif.bg.ac.rs): Faculty of Agriculture, University of Belgrade, Nemanjina 6, 11080, Zemun, Serbia Skvorc, Z. (zskvorc@sumfak.hr), Krstonosic, D. (dkrstonosic@sumfak.hr) & Franjic, J. (jfranjic@sumfak.hr): Faculty of Forestry, University of Zagreb, Svetosimuska c. 25, 10000, Zagreb, Croatia Virtual Special Feature: “Towards a consistent classification of European grasslands” (Eds. J€urgen Dengler, Erwin Bergmeier, Wolfgang Willner & Milan Chytry). Abstract Questions: How does the floristic composition of plant species of meadows and mesic pastures vary along a broad geographical gradient in the NW Balkans? How does the current phytosociological classification of the Molinio-Arrhenatheretea vegetation differ among the NW Balkan countries? Location: NW Balkans (Slovenia, Croatia, Bosnia and Herzegovina, Serbia). Methods: 3635 releves originally assigned to the class Molinio-Arrhenatheretea were classified with a beta flexible method, and the crispness of classification was checked. DCA ordination with Pignatti indicator values and climate data were applied to show the influence of site conditions on species composition. Results: The classification was best interpreted at the level of 13 clusters, but could also be interpreted at the level of three groups of clusters. The first division was according to geography and climate: the first and third groups were concentrated in the NW part, while the second was restricted to the eastern part of the study area. The most important variable was site moisture, followed by nutrients and altitude, which corresponded with a west–east direction. The first group was very diverse and included communities on the wettest and most nutrientrich sites (Potentillion anserinae, Cynosurion cristati, Calthion palustris, Molinion caeruleae, Molinio-Hordeion). The second group comprised mesophilous continental grasslands (Trifolio-Ranunculion pedati, Trifolion pallidi, Trifolion resupinati), while the third group consisted of grasslands from regions with abundant precipitation (Arrhenatherion elatioris, Deschampsion cespitosae, Pancicion serbicae, Triseto flavescentis-Polygonion bistortae). Conclusions: Our analysis can be used to unify different phytosociological classifications in different countries, also showing the transitional forms of wellknown Central European vegetation types that have a different floristic composition and ecology in the Balkans. This knowledge will enable classification of the same vegetation types in neighbouring Balkan countries that are less studied. Introduction The Balkans is a peninsula in the form of an irregular triangle that extends from Central Europe in the north to the Eastern Mediterranean in the south (Reed et al. 2004). The complexity of its physical geography and transitional location of floral (and faunal) influences have made this region a European biodiversity hotspot. The latest estimates have raised the number of autochthonous vascular plant species to 8000 in the Balkan Peninsula, which makes it one of the three (together with the Italian and Iberian Peninsulas) most important centres of floristic diversity in Europe (Stevanovic et al. 2003). The Balkans is the most species-rich region in Europe in terms of plant endemism, with 2600–2700 endemic plant taxa (Stevanovic et al. 2007). Moreover, the region is known for its very diverse vegetation, including various types of natural and semi-natural grasslands (Dajic-Stevanovic et al. 2010; Acic et al. 2013b). Grasslands are habitats dominated by graminoids and are the most widely distributed vegetation type in the 591 Applied Vegetation Science Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science cultural landscape. In addition to natural grasslands, large areas are covered with grasslands that are a product of lengthy human influence. They thrive in various ecological conditions (wet, mesic and dry) and under different management regimes (mown, grazed, fertilized), all resulting in different biological patterns (Sebastia 2004; Klimek et al. 2007; Putfarken et al. 2008; Wesche et al. 2012) and patterns of ecosystem functioning and diversity (Laliberte et al. 2010). Most grasslands represent semi-natural vegetation developed during a long history of human use. Different types of historical and current grassland use have resulted in various plant and vegetation diversity patterns. Traditionally managed semi-natural grasslands (hay meadows and pastures) are known to support a rich flora and are recognized for high species diversity in various regions of Europe, including the Balkans (Dajic-Stevanovic et al. 2010; Wilson et al. 2012). Many grassland communities are now being threatened by rapid changes in agricultural practices, especially related to the effects of either land abandonment (Pyk€al€a et al. 2005; Dajic Stevanovic et al. 2008) or intensification (Stevens et al. 2004) as contrasting management practices, whereby the latter often results in the spread of P- and N-demanding competitive grasses tolerant to mowing (Wesche et al. 2012; Ceulemans et al. 2013). In the agricultural landscapes of Central Europe (as well as in the Balkans), moist and mesic grasslands are among the habitat types that have experienced the severest losses (Prach 2008), thus attracting particular research and conservation attention. The class Molinio-Arrhenatheretea includes mown meadows and mesic pastures of temperate regions of Europe and adjacent parts of Asia (Hajkova et al. 2007). In Central Europe, several alliances are widely recognized and stable in international classifications (Arrhenatherion elatioris, Molinion caeruleae, Calthion palustris), while the classification of lowland wet meadows is less consistent (Botta-Dukat et al. 2005). In the Balkans, due to large gradients between sub-oceanic and continental climates with a Mediterranean influence, these inconsistencies are even more pronounced and also appear in well delimited syntaxa in other parts of Europe. Another reason for ambiguous classification, in addition to various climatic influences, is that some syntaxa are at the limit of their distribution. On the other hand, grasslands of Molinio-Arrhenatheretea in the Central Balkans are rich in endemics (91 taxa; Tomovic 2007). The frequent occurrence of endemic and rare plants has also been reported for several alliances of this class in the Central European region (Ruzickova et al. 2004). Species-rich mesic meadows of Molinio-Arrhenatheretea were therefore included in the European Habitats Directive (92/43/EEC; European Union 1992/1995; NATURA 2000-Codes 64 and 65). Classification of grassland vegetation of the NW Balkans is thus important for incorporating these vegetation types into the European scheme. The territory of the NW Balkans (or former Yugoslavia) has a long tradition of vegetation research, which, however, as of recently has not been transnational (Kojic et al. 1998; Trinajstic 2008; Silc & Carni 2012). This has led to syntaxonomic systems that are not comparable and, as Horvat et al. (1974) have already mentioned, different authors have classified grasslands into different syntaxa using local experience. The study area is a transitional region between different climatic influences, and this makes syntaxonomical classification more difficult. Two climatic zones (the Mediterranean and Central European) overlap in the Balkans, with a large transitional area and pronounced climate modifications, depending on the orientation of mountain massifs, lowlands, valleys and altitude, and to a large extent influenced by dominant winds. According to Polunin (1987), lowlands and valleys are of great importance for plant species distribution, since they enable advance of the mediterranean climate into the interior. Another problem is that stands are transitional between syntaxa, due to changes to or even abandonment of management. Such stands make phytosociological classification even more ambiguous. Use of large vegetation databases enables large-scale comparisons and some efforts towards identifying distinct vegetation types have already been made in the NW Balkans (Kosir et al. 2008, 2013; Silc et al. 2008; Carni et al. 2009; Marinsek et al. 2013), but not for grasslands, and in particular not for mesic grasslands. The main aim of this study was to determine the main vegetation types of the class Molinio-Arrhenatheretea in the NW Balkans, to delimit alliances geographically and ecologically and to propose a vegetation classification system on a higher level. Material A large data set of grassland vegetation releves (4615 releves originally assigned by authors into the class Molinio-Arrhenatheretea) was compiled from the territory of the NW Balkan Peninsula (Bosnia and Herzegovina, Croatia, Serbia, Slovenia). The study area extends over 216 000 km2 (13°22′W to 23°00′E and 46°54′N to 41°50′ S). The terrain is predominantly hilly, with 72% of the area (except for the large Pannonian plain) higher than 200 mÁa.s.l.; the bedrock is mainly carbonate. The climate is very diverse: a temperate warm climate predominates, while smaller regions have mountain (boreal) and true mediterranean climates (Bertic 1987). The data set consists mainly of published releves, but includes some that are unpublished (GIVD EU-HR-002, EU-RS-002, EU-SI-001). The releves are stored in TURBOVEG format (Hennekens & Schaminee 2001). Outlier Applied Vegetation Science 592 Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science Grassland vegetation of the NW Balkans U. Silc et al. analysis was processed using PC-ORD 5.0 (MjM Software Design, Gleneden Beach, OR, US) and 67 releves whose species composition deviated more than Æ2 SD from the mean calculated Euclidean distance of all plots were omitted. Releves were georeferenced a posteriori. To reduce the over-sampling bias, the data set was subsequently geographically stratified by 6′ latitude 9 10′ longitude grid cells and ten releves were selected from each grid cell by heterogeneity-constrained random resampling (Lengyel et al. 2011) to obtain balanced floristic diversity. Finally, 3635 releves were included in the analysis. Species nomenclature was checked and synonyms and taxa determined at various ranks were aggregated to a common taxonomic level (e.g. Agrostis stolonifera agg. = A. gigantea, A. stolonifera; Brachypodium pinnatum agg. = B. pinnatum, B. rupestre; Bromus racemosus agg. = B. racemosus, B. commutatus; Carex flava agg. = C. flava, C. lepidocarpa; Centaurea jacea agg. = C. jacea, C. angustifolia, C. macroptilon; Festuca pratensis agg. = F. pratensis, F. arundinacea; Galium mollugo agg. = G. album, G. mollugo; Leucanthemum vulgare agg. = L. vulgare, L. praecox; Polygonum aviculare agg. = P. aviculare, P. arenastrum; Vicia sativa agg. = V. angustifolia, V. sativa; Vicia pannonica s. lat = V. pannonica, V. striata). Records of species determined to the genus level and bryophytes and lichens were deleted from the data set since they were not consistently sampled by all of the authors. Species cover values in original releves were estimated on different scales. They were a posteriori transformed to percentages and square-rooted. Climatic variables (annual temperature, precipitation and BIO 18 – precipitation of the warmest quarter) were subjectively selected, since we presumed that they have strong effects on species composition. They were compiled for each releve from the WorldClim database (Hijmans et al. 2005). Environmental indicator values of Pignatti (2005) were used for ecological interpretation of gradients. Unweighted mean indicator values were calculated for each releve and, in the same way, for columns in the synoptic table. Methods We classified the data set (3635 releves) using cluster analysis in the PC-ORD 5.0. The Sørensen index as the distance measure and beta flexible (^a = À0.25) for group linkage were used. We made several classifications with different numbers of clusters of releves. We used the OptimClass method (Tichy et al. 2010) for identifying the optimal partition and the peak of the OptimClass1 curve showed the optimal number of clusters is 13 at threshold P < 10EÀ10 . We accepted this classification with 13 clusters as being the ecologically soundest. Other classifications with more clusters produced groups with ambiguous ecological and syntaxonomic significance. The synoptic table was produced in the JUICE program and the phi (u) coefficient was used as the measure of fidelity. Each cluster was compared to the remaining releves in the data set, which were taken as a single undivided group. Since the clusters consisted of unequal numbers of releves, higher u values for larger clusters were expected. To avoid that, each of the 13 clusters was virtually equalized to 1/13 of the size of the entire data set (Tichy & Chytry 2006). The threshold of the u value was subjectively selected at 0.10 for a species to be considered diagnostic. This threshold was considered to be optimal for interpreting a single cluster and for preventing inflation of diagnostic species. Relationships between clusters and environmental indicator values were visualized using DCA ordination, in which the square-rooted percentage covers of species were used. The mean ecological indicator values (based on Pignatti 2005) were plotted a posteriori on the DCA ordination diagram. Ordination results are presented on spider plots, in which each releve is linked to the centroid of its cluster by a line. Analysis was performed in R (R Foundation for Statistical Computing, Vienna, AT; v 2.15.2, http://www. r-project.org) using vegan package (http://cc.oulu.fi/~ jarioksa/softhelp/vegan.html). Results Classification Classification could first be interpreted at the level of three groups of clusters (Fig. 1, clusters 1–6, 7–9 and 10–13; Table 1), which reflected geographic and climatic factors, with the first and third group concentrated in the NW part and the second group restricted to the E part of the study area. The first group is very diverse and includes the wettest communities on the one hand and the most nutrientrich communities on the other. The second group comprises mesophilous continental grasslands, while the third group of clusters consists of grasslands on deeper soils from regions with high precipitation. The most meaningful and finer classification is at the level of 13 clusters (Fig. 1, Table 1). Cluster 1 comprises nitrophilous, semi-ruderal grasslands along water bodies dominated by Agrostis stolonifera agg. Cluster 2 represents typical vegetation of the alliance Cynosurion cristati from temperate Europe. Communities are dominated by species adapted to trampling (Lolium perenne, Plantago major), while the species Cynosurus cristatus in the NW Balkans is characteristic for the association Bromo-Cynosuretum (Cluster 12). 593 Applied Vegetation Science Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science U. Silc et al. Grassland vegetation of the NW Balkans Cluster 3 contains releves of the alliance Calthion palustris, dominated by hygrophilous herbs. They are found on wet, nutrient-rich soils with a large altitudinal range (they are found in lowlands and up to 1800 m). Cluster 4 comprises vegetation dominated by Molinia caerulea agg. distributed mostly in Slovenia with some occurrences also in the south (Caltho-Alopecuretum in Vojvodina and at higher altitudes in Serbia, with a mix of Deschampsia caespitosa and Polygonum bistorta). Stands are wet, and compared to other clusters nutrient-poor and acidic. Cluster 5 corresponds to the Illyrian-Mediterranean alliance Molinio-Hordeion secalini, which is found on Karst poljes. It is geographically limited to Slovenia, Croatia and Bosnia and Herzegovina. Cluster 6 represents a rare plant association Scirpo holoschoeni-Salicetum rosmarinifoliae found on sandy sites along rivers and classified into the Molinion caeruleae alliance. Communities are dominated by Salix repens and xeric grassland species. Cluster 7 includes wet lowland grasslands in the eastern continental part of the NW Balkans (E Croatia and central Serbia). In addition to grasses, the most important species group consists of clovers (Trifolium patens, T. pallidumi T. resupinatum) and other Fabaceae (Medicago arabica, M. polymorpha, Lathyrus tuberosus). Cluster 8 covers mesophilous grassland vegetation on the Pannonian plain that can thrive in sites with high variability of soil moisture and slight salinity. The grass species Poa angustifolia, Poa palustris and Alopecurus pratensis are characteristic for the communities classified into the alliance Trifolio-Ranunculion pedati. Cluster 9 comprises plant communities classified into the Balkan sub-halophytic alliance Trifolion resupinati. These are sub-Mediterranean lowland meadows in the S and SE part of the research area. Cluster 10 includes releves with the largest altitudinal range. There are communities from higher altitudes (Pancicion serbicae) as well as stands that are poor in characteristic species or were classified to higher syntaxa (mainly into the order Arrhenatheretalia) and are similar in floristic composition to stands from higher altitudes. The map of this cluster therefore shows mixed geographic distribution with communities of high altitudes and depauperate stands found in lowlands. Cluster 11 consists of typical grasslands of Central Europe that are classified into alliances Arrhenatherion elatioris, Triseto flavescentis-Polygonion bistortae and Poion supinae and dominated by the grasses Arrhenatherum elatius, Trisetum flavescens, Dactylis glomerata, Avenula pubescens. Cluster 12 represents widespread wet stands of the alliance Arrhenatherion elatioris, mostly the association BromoCynosuretum comprising lowland grasslands temporarily flooded in spring. Stands are characterized by Holcus lanatus and Cynosurus cristatus. In Central Europe, the latter species is characteristic for trampled and frequently mowed grass- lands. Fig. 1. Classification dendrogram of grassland dataset (3635 plots). 1 – Potentillion anserinae, 2 – Cynosurion, 3 – Calthion, 4 – Molinion, 5 – MolinioHordeion secalini, 6 – Scirpo holoschoeni-Salicetum rosmarinifoliae, 7 – Trifolion pallidi, 8 – Trifolio-Ranunculion pedati, 9 – Trifolion resupinati, 10 – Pancicion serbicae & species poor Arrhenatheretalia, 11 – Arrhenatherion s.str. & Triseto flavescentis-Polygonion bistortae, 12 – Bromo-Cynosuretum, 13 – Deschampsion. The numbers of clusters refer to Table 1 and the number of releves included in each cluster is indicated. Applied Vegetation Science 594 Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science Grassland vegetation of the NW Balkans U. Silc et al. Table 1. Synoptic table of Molinio-Arrhenatheretea grasslands in the NW Balkans. The frequency values are shown, shaded are species with phi values higher than 0.1. Only five species with highest fidelity are presented. Cluster 1 2 3 4 5 6 7 8 9 10 11 12 13 No. of releves 240 128 279 311 198 21 452 199 258 457 473 346 273 % releves for country Slovenia 31 25 23 68 10 0 5 0 0 24 44 33 55 Croatia 42 49 17 4 64 0 12 21 0 29 55 66 38 Bosnia and Herzegovina 4 0 1 1 26 0 3 0 0 11 0 0 0 Serbia 24 26 59 26 1 100 81 79 100 36 1 0 7 Cluster 1: Potentillion anserinae Agrostis stolonifera agg. 93 38 21 23 22 – 29 18 10 7 3 26 25 Mentha longifolia 38 6 14 3 – – 6 2 6 6 5 1 1 Juncus inflexus 32 7 13 4 1 – 2 1 – 1 – 2 4 Alopecurus geniculatus 10 – 1 – – – – – – – – – – Rorippa sylvestris 46 22 8 1 6 – 21 20 25 4 1 1 2 Cluster 2: Cynosurion Lolium perenne 22 85 2 – 8 – 9 4 62 15 23 17 2 Cynodon dactylon 12 56 2 – 5 – 3 18 1 4 1 1 1 Plantago major 30 64 6 3 2 – 9 10 9 12 4 4 2 Trifolium repens 47 88 27 4 7 – 28 26 38 42 35 36 20 Poa annua 11 29 – – – – 1 4 – 8 1 1 – Cluster 3: Calthion Scirpus sylvaticus 3 – 45 3 – – 1 – 4 2 1 4 5 Filipendula ulmaria 5 – 34 29 3 – 1 – – 4 2 13 25 Eriophorum latifolium – – 21 15 1 – – – – 1 – – 1 Equisetum palustre 3 – 37 22 2 10 2 10 6 2 3 9 15 Caltha palustris 3 – 34 10 – – 1 4 1 3 – – 4 Cluster 4: Molinion coeruleae Molinia caerulea agg. – – 15 93 31 29 – – – 2 2 3 15 Schoenus ferrugineus – – – 15 – – – – – – – – – Potentilla erecta 2 – 28 73 8 – 1 1 – 13 15 26 44 Succisa pratensis 1 – 11 49 5 – 1 – – 1 1 19 29 Sanguisorba officinalis – – 10 48 20 – 4 1 1 1 3 13 24 Cluster 5: Molinio-Hordeion secalini Scilla litardierei – – – 1 47 – – – – – – – 2 Deschampsia media – – – – 26 – 1 – – – – – – Peucedanum coriaceum – – – 3 39 – 1 – – – – – 6 Centaurea pannonica 1 – – 8 33 – 1 – – 1 1 4 1 Sesleria caerulea – – – – 17 – 1 – – – – – – Cluster 6: Scirpo holoschoeni-Salicetum rosmarinifoliae Salix rosmarinifolia – – – 4 3 100 – – – – – 1 1 Calamagrostis epigejos – 1 1 3 – 100 2 2 – 5 2 1 2 Scirpus holoschoenus – – – 3 1 71 – – – – – – 1 Inula salicina – – 1 4 8 90 11 8 – 1 4 2 6 Scabiosa ochroleuca – – – 2 – 86 – 2 – 2 – – – Cluster 7: Trifolion pallidi Medicago arabica 1 1 – – – – 19 1 1 – – 1 – Trifolium pallidum – – 1 – 1 – 17 9 8 2 1 1 1 Poa trivialis 20 2 32 10 1 – 49 16 – 13 25 32 19 Clematis integrifolia – – 1 1 5 – 16 11 – – 1 1 – Poa pratensis 4 5 5 7 2 – 61 22 14 29 53 47 29 Cluster 8: Trifolio-Ranunculion pedati Poa angustifolia – – – 1 4 5 – 28 – 3 1 1 3 Poa palustris 3 2 10 1 1 – 1 34 – – 1 1 8 Euphorbia lucida – – – – – – – 24 – – – – – Festuca pseudovina 1 14 – – 5 – 2 25 – 2 1 – – Trifolium angulatum 2 – – – – – 1 20 – – – – – 595 Applied Vegetation Science Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science U. Silc et al. Grassland vegetation of the NW Balkans Cluster 13 includes communities dominated by Deschampsia cespitosa on clay soils with alternating wet and dry phases. These grasslands are found in S Slovenia, the continental part of Croatia and in some localities at higher elevations in Serbia. Ordination analyses The first DCA axis shows the gradient of altitude and nutrients, and this gradient also corresponds to a W–E direction (Figs 2 and 3). Temperature and BIO18 (precipitation of the warmest quarter) as climatic variables also correspond to the first axis. The most important variable is moisture of the site and coincides with the second DCA axis; it is striking that continentality shows an opposite trend to mois- ture. Discussion Moisture and nutrients (fertility) were found to be the most important gradients determining the floristic composition of mesic grasslands in the NW Balkans. This is congruent with several studies of this type of grassland (Havlova et al. 2004; H€ardtle et al. 2006; Zelnik & Carni 2008). Next is the temperature (warmth) of the site, which correlates with climatic variables, in particular precipitation of warmest quarter of the year (Appendix S1). Climatic variables, especially those linked to precipitation, are important in forming plant communities, and this gradient corresponds to the NW–SE gradient along the peninsula, linking Central European communities to Pannonian and (sub)-Mediterranean ones. The importance of climate for the species composition of wet grasslands that are saturated by surface or groundwater has already been demonstrated (Ilijanic 1973; Hajek et al. 2008). The vegetation structure and species composition in SE European peninsulas is strongly influenced by biogeographic and ecological differences (Blasi et al. 2012; Elias et al. 2013). In addition to site conditions, management is very important for the establishment of different grassland communities (Dierschke & Briemle 2002; Zelnik 2005). Different management practices, such as cutting, grazing, application of artificial fertilizers, sowing species, can significantly alter species composition (Waldhardt & Otte 2003; Havlova et al. 2004; Drobnik et al. 2011), which results in different grassland types (e.g. species-poor comTable 1. (Continued). Cluster 1 2 3 4 5 6 7 8 9 10 11 12 13 Cluster 9: Trifolion resupinati Poa trivialis subsp. sylvicola – – – 1 17 – 1 – 83 – 1 1 1 Ranunculus velutinus – – – – – – 4 – 53 – – – – Trifolium balansae – – – – – – – – 25 – – 1 – Alopecurus rendlei – – – – 5 – 6 – 53 – 1 5 2 Tragopogon orientalis – – – 1 1 38 7 1 61 6 17 8 1 Cluster 10: Pancicion + Triseto-Polygonion bistortae + species poor Arrhenatheretalia Agrostis capillaris 1 – 9 2 12 – 2 – 1 33 7 18 4 Festuca rubra agg. – – 4 18 9 – 3 – – 50 27 34 25 Hypochaeris maculata – – – – – – – – – 13 1 – – Silene sendtneri – – – – – – – – – 11 – – – Pimpinella serbica – – – – – – – – – 8 – – – Cluster 11: Arrhenatherion Arrhenatherum elatius – – 1 1 – – 4 – – 28 87 19 – Trisetum flavescens – – 1 1 – – 1 – 1 18 75 32 1 Dactylis glomerata 5 5 2 10 6 – 9 4 1 49 85 31 7 Salvia pratensis – – – – 1 – 6 2 – 9 43 2 – Knautia arvensis – – – 2 – – 5 1 – 16 47 12 – Cluster 12: Bromo racemoso-Cynosuretum cristati Cynosurus cristatus 4 5 27 13 16 – 38 – 44 39 32 86 42 Gaudinia fragilis – – 1 – – – 1 – – 1 3 23 3 Rhinanthus minor 1 – 25 11 24 – 4 3 27 13 34 56 18 Ranunculus acris 12 2 35 50 39 – 28 13 40 24 72 94 75 Ononis arvensis 1 9 2 1 – – 8 3 5 – 18 36 5 Cluster 13: Deschampsion caespitosae Deschampsia cespitosa 6 – 37 30 21 – 3 4 5 8 5 30 77 Agrostis canina agg. 2 – 5 10 – – 2 10 4 1 – 16 47 Succisella inflexa – 2 8 5 1 – 1 – – – – 7 40 Ranunculus flammula 2 – 6 4 1 – 2 – – – – 8 36 Juncus conglomeratus 1 – 24 16 2 – 1 4 – 1 1 24 49 Applied Vegetation Science 596 Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science Grassland vegetation of the NW Balkans U. Silc et al. munities). In large-scale analyses of vegetation databases, it is difficult to incorporate management into the analysis as an explanatory variable, and such wide geographic and climatic analyses are rare (Moog et al. 2002; Wellstein et al. 2007). The syntaxonomic scheme of the class Molinio-Arrhenatheretea (Appendix S2) is the first attempt of such scope in the NW Balkans based on releve material from a large database and on multivariate methods (classification and ordination), and to the association level. The Balkans is a transitional area in terms of climate and phytogeography, and classification of certain grassland syntaxa is therefore very difficult. Certain species with clear diagnostic values in Central Europe, for example, are at the limit of their distribution here and their coenological optima shifts. Rather than offering definite answers, our analysis therefore generates new questions about the syntaxonomic system. Horvatic (1939) placed the geographic border between the alliances Molinion caeruleae and Deschampsion cespitosae in SE Slovenia and this is also confirmed by our analysis (Fig. 3). In the NW Balkans, Molinion caeruleae is found in the NW part (e.g. Slovenia), while Deschampsion cespitosae is limited mainly to the continental part of Croatia along the Sava River to the river Orljava (Ilijanic 1973), but occurs also in Serbia and Bulgaria. Humid climate, higher altitudes and higher amounts of organic matter are more characteristic of the Molinion caeruleae alliance (Zelnik & Carni 2013). The diversity of Molionion caeruleae is higher in the NW Balkans than in neighbouring regions. One reason is the influence of different phytogeographic regions on species composition; another is the traditional classification into several narrower associations (acido- and basophilous, on Sphagnum mires). Classification also supports the findings of Botta-Dukat et al. (2005) that Cnidion venosi and Deschampsion cespitosae cannot be interpreted as two geographically vicariant alliances, Pannonian and Illyrian, respectively, as proposed by Ellmauer & Mucina (1993). The alliance Agrostion albae is classified within the alliance Deschampsion cespitosae in several national surveys (Chytry 2007; Borhidi et al. 2012), while it was classified as a separate alliance in Serbia (Kojic et al. 1998). In our numerical classification, communities of Agrostion albae from Serbia are classified into Potentillion anserinae (Acic et al. 2013a). There is a striking difference in the distribution pattern of Deschampsion cespitosae in the Balkans. In the NW part of the peninsula, a typical region of this alliance, stands are found on flooded lowlands up to 400 mÁa.s.l. (Ilijanic 1973; Botta-Dukat et al. 2005), while in the eastern part of the Balkans they are found at higher elevations (700– 1000 mÁa.s.l.; Hajek et al. 2008; Milosavljevic et al. 2008; Randelovic & Zlatkovic 2010). It was previously considered that this alliance is absent to the east of the river Orljava and very rare in Serbia (Ilijanic 1973; Kojic et al. 1998) but these stands were later included in Molinietum caeruleae (Kojic et al. 2004). In the southern part of the study area, Molinia and Deschampsia occur together in stands, and the difference in nutrient availability is responsible for their habitat differentiation (Hajek et al. 2008). In the central Balkans, Molinia and Deschampsia are found at higher elevations, where climatic conditions resemble those in Central European lowlands. Cynosurus-dominated communities are very common in the Balkans, where several associations with Cynosurus as a characteristic species are described. In the numerical analysis, these Cynosurus-dominated communities are classified into two distinct clusters. The first is the Cynosurion cristati alliance typical of temperate Central Europe, on grasslands that are intensively grazed and mown. Another Cynosurus community is the association Bromo racemosi-Cynosuretum found in continental Croatia and Slovenia, which develops on temporarily inundated soils and is the most widespread mown meadow in the region (Horvatic 1930). The Cynosurion cristati alliance is widespread in W and Central Europe, and concentrated in the sub-montane and montane zone towards the SE (Zuidhoff et al. 1995); it is represented by the well-delimited association Lolio perennis-Cynosuretum. The presence of the species Cynodon dactylon indicates the more southern and 0 0 –3 –2 –1 1 2 3 –3–2–11234 DCA1 DCA2 1 2 3 4 6 7 9 10 11 12 13 Light Temperature Continentality Moisture Reaction Nutrients Annual temperature Precipitation Bio 18 Altitude Fig. 2. DCA ordination of the whole dataset. Centroids of clusters from the classification are indicated and ecological variables (ecological indicators and the most important climatic variables) are presented. Eigen values of axes are: 1st axis 0.449 and 2nd axis 0.405 and total inertia 12.784. 597 Applied Vegetation Science Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science U. Silc et al. Grassland vegetation of the NW Balkans warmer character of these stands compared to this type of vegetation in Central Europe. The position of BromoCynosuretum is unclear; according to (Stancic 2008) characteristic species have a broad ecological range and should be divided into a number of associations. In our analysis, these stands (together with some wet Arrhenatherion elatioris stands) are separated as a single cluster with a transitional position between Cluster 5 and 10 in the DCA diagram (Fig. 2), as also pointed out by Lengyel et al. (2012). The species composition and DCA analysis suggest that these grasslands should be classified within the alliance Arrhenatherion elatioris. Another possibility is classification into the alliance Deschampsion cespitosae but there are more species present that are characteristic for the alliance Arrhenatherion elatioris. Classification of Bromo-Cynosuretum into higher syntaxa is therefore not clear; various authors classify it into the alliance Cynosurion cristati or Arrhenatherion elatioris (Kojic et al. 1998; Trinajstic 2008; Velev et al. 2011a). Stancic (2008) indicated that some of the releves of Bromo-Cynosuretum should be classified into Arrhenatherion elatioris and some into Deschamspion cespitosae. Cluster 11 comprises the alliances Arrhenatherion elatioris and Triseto flavescentis-Polygonion bistortae, which are typical of the NW part of the study area, which is already part of the SE Alps. Releves of these two alliances merged into one cluster since their sites are similar in terms of moisture and nutrients (Heged€usova et al. 2011). Communities of Arrhenatherion elatioris from the south are less mesic and lack characteristic species, while the alliance Triseto flavescentis-Polygonion bistortae is not present in the central Balkans (Apostolova et al. 2007). It is replaced by the alliance Arrhenatherion elatioris, which occurs at elevations of 700– 1600 m. The altitudinal shift of plant communities towards the south of the Balkans is well known (Horvat et al. 1974; Hajek et al. 2008) and is the reason for the ambiguous classification of vegetation that spreads over the long biogeographic gradient. Fig. 3. The distribution of releve´s included in particular clusters. The numbers of clusters refer to Table 1. Applied Vegetation Science 598 Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science Grassland vegetation of the NW Balkans U. Silc et al. The association Arrhenatheretum s. lat. is widespread in Central and Western Europe, and the dominant species gives the stands an easily recognizable physiognomy. In many cases, stands were classified as belonging to Arrhenatheretum s. lat. because of the presence of the dominant grass species. The association changes towards the south and communities become more ruderal (Velev et al. 2011b). In Serbia these communities were previously considered as sown grasslands (Jovanovic-Dunjic et al. 1986) or were found mostly along roads (Parabucski 1990). They are also less commercially important, found in untypical ecological conditions in the Pannonian region (Vojvodina) (Kojic et al. 2005) or in the montane belt in central Serbia (Acic et al. 2013b). Arrhenatherion elatioris stands from Serbia are therefore in the same cluster as ruderalized mesic grasslands from the northern part of the study area. On the other hand, stands of the alliance Arrhenatherion elatioris from Bulgaria are more similar to those of Central European (Velev et al. 2011b). Pancicion serbicae is an alliance found at higher elevations, rich in endemic species and with a Dinaric distribution (Lakusic 1966). Pancicia serbica appears in various plant communities (forest and non-forest) and has a disjunct distribution in the Balkans (Obratov & Dukic 1998). Despite endemic species, the alliance was not clearly delimited in our analysis and merged with speciespoor stands and stands classified at higher syntaxonomic levels without characteristic species. The factors filtering the species composition at higher elevations seem similar to those of human-disturbed sites at lower altitudes. Grazing disturbance and altitudinal stress resemble high human impact in the lowlands (e.g. road verges, intensive mowing). Management can blur delimited communities, especially if there is a combination of hay-cutting and grazing or a change of pasture into meadow (or vice versa) (Havlova et al. 2004). The alliance Trifolion pallidi is mainly found in eastern Croatia and central Serbia and the alliance Trifolion resupinati is limited to southern Serbia, where the climate is warmer and more arid. Our analysis shows the distribution of Trifolion pallidi to be the most eastern part of Serbia, on the border with Bulgaria, although it has not so far been identified in Bulgaria (Elias et al. 2013). It is linked to the climax vegetation Quercion frainetto, and when Ilijanic (1969) described the alliance, he assumed its distribution in Bulgaria and Romania. Short descriptions of the alliances On the basis of the literature review and our own results, we present a unified syntaxonomic list, which is critically commented and highlights the syntaxonomic problems for further analysis (Appendix S2). Each alliance is presented in brief. Molinion caeruleae These grasslands are found on wet or moist soils, sometimes even on peaty soils. The water table is high during one period of the vegetation season. Molinion grasslands are concentrated in Slovenia, with some localities in Pannonia and central Serbia. The characteristic and dominant species is Molinia caerluea agg., accompanied by Schoenus ferrugineus, Potentilla erecta and Sanguisorba of- ficinalis. Calthion palustris Wet grasslands and tall herb communities that are frequently unmanaged. They are found on flat lands along streams or on saturated soils near headwaters. Stands are distributed in Slovenia, Croatia and the mountainous parts of southern Serbia. The predominant species are Scirpus sylvaticus, Filipendula ulmaria, Juncus effusus and Eriophorum latifolium (the last species is characteristic for specific stands in Serbia). Deschampsion cespitosae Meadows on alluvial lowlands that are flooded from rainwater and less from water courses. Soils have impermeable layers and water stagnates for some period. These meadows occur in Slovenia and Croatia, with one location in SE Serbia. Meadows are dominated by Deschampsia cespitosa and Agrostis canina agg., other characteristic species are Succisella inflexa, Ranunculus flammula and Gratiola officinalis. Molinio-Hordeion secalini Stands of this alliance are typical grasslands from the humid part of the sub-Mediterranean region, mostly on periodically flooded Karst poljes and locally on some islands. Their distribution stretches from Slovenia through Croatia to Bosnia and Herzegovina. Characteristic species are Scilla litardiei, Deschampsia media, Peucedanum coriaceum and Plantago altissima. Trifolion resupinati The alliance includes lowland wet grasslands of the subMediterranean part of the central Balkans (southern Serbia in the study area, with the centre of distribution in Macedonia). The climate is extreme and sites dry out in summer. The main species are Poa sylvicola, Trifolium 599 Applied Vegetation Science Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science U. Silc et al. Grassland vegetation of the NW Balkans resupinatum and several other species of the genus Trifolium (T. balansae, T. nigrescens, T. fragiferum). Trifolion pallidi The alliance consists of wet flooded meadows with less drought in summer than Trifolion resupinati, and colder winters than Molinio-Hordeion secalini. The centre of distribution of the alliance is eastern Croatia and western Serbia. Characteristic species are Medicago arabica, Trifolium patens, Festuca pratensis agg. and Trifolium pallidum. Trifolio-Ranunculion pedati The alliance includes grasslands of a mesic sub-halophytic character. The alliance is restricted to the Pannonian plain. Characteristic species are Poa angustifolia, P. palustris and Trifolium angulatum and accompanied by the halophytes Aster canus, Limonium gmelinii and Podospermum canum. Cynosurion cristati Intensively managed grasslands (pastures) on fertile soils found in the Central European floristic region of the NW Balkans (Slovenia, Croatia and Vojvodina). The main species are Lolium perenne, Trifolium repens, Cynodon dactylon and Trifolium fragiferum. Arrhenatherion elatioris The alliance includes mesic non-flooded meadows, regularly mown and often fertilized. It is most common in Central Europe; in the study area it is common in Slovenia and Croatia, while in southern parts these grasslands are also found in the mountain belt. Diagnostic species are Arrhenatherum elatius, Dactylis glomerata, Galium mollugo agg. and Pastinaca sativa. Alchemillo-Ranunculion repentis This vegetation type includes moderately trampled mesophilous communities often in shaded sites. The alliance is only found in the northern part of the study area (Slovenia and Croatia). The characteristic species are Prunella vulgaris, species characteristic of trampled habitats and the neophytes Juncus tenuis and Duchesnea indica. Potentillion anserinae The alliance comprises stands along water bodies with alternating wet and dry phase. They are distributed in the northern part of NW Balkans and on the Pannonian lowlands. Stands are dominated by Agrostis stolonifera agg., Mentha longifolia and Juncus inflexus. Triseto flavescentis-Polygonion bistortae The alliance comprises mostly pastures from submontane and montane belts (up to 1500 mÁa.s.l.) from northern Slovenia. Stands are dominated by Trisetum flavescens, other diagnostic species are Astrantia major, Bromus erectus and Rhinanthus alectorolophus. Pancicion serbicae These are mesophilous grasslands of the upland and subalpine belts (1100–1800 m) in mountain ranges of Bosnia and Herzegovina, Kosovo, southern Serbia and also Montenegro. The characteristic species of this endemic Dinaric alliance are Anemone narcissiflora, Crepis aurea var. bosniaca, Pimpinella serbica and Phleum alpinum. Poion supinae These are meadows that are mown once a year and then grazed, in the mountain belt (800–1300 mÁa.s.l.). They are found in Croatia and probably also in Slovenia. Stands are dominated by Trisetum flavescens accompanied by Alchemilla xanthochlora and species of the Arrhenatherion elatioris alliance. Acknowledgements We are grateful to Ladislav Mucina who allowed us to use the unpublished EuroVegChecklist. We thank Iztok Sajko for producing the maps and for data extraction in GIS, and Andrej Rozman for help with graphs. Martin Cregeen kindly checked our English. 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Syntaxonomic checklist of the MolinioArrhenatheretea class in the NW Balkans. Appendix S3. Full synoptic table in pdf and csv format. 603 Applied Vegetation Science Doi:10.1111/avsc.12094 © 2014 International Association for Vegetation Science U. Silc et al. Grassland vegetation of the NW Balkans